Phase-space density constraints on the formation of bulges from discs

Details Phase-space density constraints on the formation of bulges from discs Phase-space density constraints on the formation of bulges from discs

Feb 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998mnras.293..429w&link_type=abstract

Monthly Notices of the Royal Astronomical Society, vol. 293, p. 429

Astronomy and Astrophysics

Astronomy

13

Space Density, Galactic Bulge, Star Distribution, Galactic Structure, Milky Way Galaxy, Galactic Evolution, Constraints

Scientific paper

The colors of stellar bulges and of inner stellar disks are comparable and consistent with rather similar mean metallicities and ages. Indeed, the mean chemical abundances of the Milky Way bulge and old disk are approximately equal. Further, the scalelengths of disks and bulges are correlated. These observations imply a close relationship between disks and bulges, and may support models in which stellar bulges form from stellar disks. The present paper discusses constraints on this scenario from the stellar phase-space density of bulges and of disks. Phase-space density cannot increase in the absence of collisional processes. We show here that the maximum phase-space density of galactic bulges is higher than that of inner disks, arguing that instabilities of purely stellar disks cannot form bulges. Rather, the high densities of bulges probably reflect gaseous dissipation. Gas inflow from the disk would complicate the interpretation of the similarities in stellar colors between disks and bulges. Gas inflow from the stellar halo, if one exists, may be favored on angular momentum grounds, but this means of formation of the bulge would provide no explanation for the relationships between disk and bulge in any one galaxy. At least in the Milky Way, the metallicity distribution of the bulge is not consistent with the bulge being built up from the dense regions of accreted satellite galaxies and/or globular clusters.

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